[DataFrame] Error checking on Pandas version

[devin-petersohn]

We need better reporting for issues with the Pandas version on a user's system.

[robertnishihara]

How about in dataframe.py, we add a line like

# Pandas must be at least version 0.22.0.
pd_major = int(pd.__version__.split(".")[0])
pd_minor = int(pd.__version__.split(".")[1])
if (pd_major == 0) and (pd_minor < 22):
    raise Exception("Your Pandas version is less than 0.22.0. Please "
                    "update Pandas to the latest version.")

[devin-petersohn]

I was thinking it belongs in dataframe/__init__.py before we start the Ray cluster.

[robertnishihara]

That's probably better.